class Ship():
    def __init__(self, ai_settings, screen):
        """初始化飞船并设置其初始位置"""
        self.screen = screen
        self.ai_settings = ai_settings
        # 加载飞船图像并获取其外接矩形
        self.image = ai_settings.ship_image
        self.rect = self.image.get_rect()
        self.screen_rect = screen.get_rect()
        # 将每艘新飞船放在屏幕底部中央
        # 属性 center、centerx 或 centery
        # 属性 top、bottom、left 或 right
        self.rect.centerx = self.screen_rect.centerx
        self.rect.bottom = self.screen_rect.bottom
        # 在飞船的属性 center 中存储小数值
        self.center = float(self.rect.centerx)
        # 移动标志
        self.moving_right = False
        self.moving_left = False
        # 发射子弹标志
        self.openfire = False

    def center_ship(self):
        """居中飞船，用于游戏状态重置时使用"""
        self.center = self.screen_rect.centerx

    def update(self):
        """根据移动标志调整飞船位置"""
        # 两个 if，不用 elif，让左右按键的优先级相同
        # 根据飞船的左右坐标，保证不出画面
        if self.moving_right and self.rect.right < self.screen_rect.right:
            self.center += self.ai_settings.ship_speed_factor
        if self.moving_left and self.rect.left > 0:
            self.center -= self.ai_settings.ship_speed_factor
        # 根据 self.center 更新 rect 对象
        self.rect.centerx = self.center

    def blitme(self):
        """在指定位置绘制飞船"""
        self.screen.blit(self.image, self.rect)
